Vaadin utilises Java for the creation of web applications.
A GMF project comes in the form of eclipse PLUGINS.

You can not integrate the editor in your application, because it is meant to run in eclipse/desktop... Try to build the model editor with some javascript libraries instead.

Now on the other hand, if you create the GMF editor as an RCP, you can run it outside of eclipse, but still you can not integrate it in your web app. However, you can offer it for download to the users.